Three Dimensional Turbulent Fluid Flow and Heat Transfer Mathematical Model for the Analysis of a Continuous Slab Caster

Abstract

Continuous casting of slab caster of Tata Steel has been simulated using a three dimensional mathematical model based on considerations of fluid flow, heat transfer and solidification for better understanding of the process. Liquid metal comes in the mould by bifurcated nozzle. The principal model equations are momentum and heat balances. In various zones, different standard boundary conditions have been used. In the mould region, Savage and Prichard expression for heat flux has been used. In the spray cooling zone, heat transfer coefficient for surface cooling of the slab has been calculated by knowing the water flow rate and nozzle configuration of plant. The turbulence in the molten metal has been modelled by the Realizable k-e model. CFD software (Fluent) has been used for the solution of equations to predict the velocities in the molten pool of the slab, temperature of the entire volume of the slab, heat transfer coefficient in the mould region, heat flux in the spray and radiation region and shell thickness. The variables studied are different casting speed.KEY WORDS: slab caster; turbulence; solidification; shell profile; CFD; radiation cooling; spray cooling; heat flux; heat transfer coefficient; mathematical modelling; steel casting; realizable k-epsilon model. ISIJ International, Vol. 47 (2007), No. 3, pp. 433-442 433 © 2007 ISIJ austenite-ferrite phase transformation, which is accompanied by a sizeable volume change should not occur. To meet the above criteria, after certain length of spray cooling, the strand is allowed to be radiant cooled. The dimensions of the caster are given in Table 1. The spray zone length has been sub divided into six regions for flexibility of cooling. The first is spray ring region (Zone 0) just after the mould and having only water flow. In the narrow face of the slab, the spray ring region (Zone 0 N&S) is also having only water flow. After this region, there is no forced cooling on the narrow face. After spray ring region other spray zones are named as 1A, 1B, Zone 2, Zone 3, Zone 4 and Zone 5 as mentioned in Table 1. Slab cast should be free from surfaces and internal cracks. For a given composition of steel, solidification in the slab casting will depend on fluid flow and heat transfer in different zones. In the mould region, the total heat transfer can be easily obtained by knowing difference of temperature between the inlet and the outlet of water passing through mould cooling jacket and its flow rate. Theoretically, it is difficult to get the heat transfer along the mould length because of air gap formation between mould and slab, resistance of heat flow due to shell formation, mould plate, water-copper plate, thermal contraction of slab and mould plate, bulging due to liquid height pressure.2-6) Singh and Blazek 7) have experimentally measured the heat transfer profile along the mould length by using a bench scale casting facility. Mould was stationary, unlike the actual caster. They have shown the effect of carbon content, casting speeds, pouring practice, mou...

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